When a man gets a vasectomy, it doesn't mean that he's guaranteed never to conceive a child. There is a failure rate for vasectomies of between half a percent and one percent.

The time of most risk after a man has a vasectomy is in those first few months after it happens. Usually, your doctor will have you go through a number of tests of your semen in the weeks and the months after your vasectomy.

The purpose of these, of course, is to check your semen for the presence of sperm. The highest odds of conceiving a child are at this time. It may take as many as 60 ejaculations before any sperm that still remains in the man's body stops showing up in the semen. In some cases, even after a semen test is taken in which no sperm are found, a man may later become potent and start having sperm in his semen again.

Any number of things can be responsible for this. They can include a technical error in the vasectomy procedure, for example. In some cases, the ends of the vasa that are cut can actually grow back together on their own. In other cases, an opening can develop in the vasa that will allow sperm to come through.

For women, the chances of getting pregnant after sterilization are similar to the chances for men. Having a tubal ligation or having your "tubes tied" closes the fallopian tubes, through cutting, burning, or blocking with clips, bands, or rings.

This blocking keeps the egg from traveling from the ovary to the uterus. In addition, it prevents sperm from reaching the fallopian tube. Tubal ligation is around 99.5% effective at preventing pregnancy.

There are a couple of important factors to consider when thinking about surgical sterilization to reduce your chances of getting pregnant. Surgical sterilization does not protect against AIDS or other sexually transmitted diseases.

Additionally, while it is possible to have surgical sterilization reversed, the reversal is not always successful. If you intend to have children in the future, surgical sterilization is probably not the best option for you.